Direct plating method and solution for palladium conductor layer formation

ABSTRACT

A surface of an object to be plated is subjected to a treatment for palladium catalyst impartation to impart a palladium catalyst to the surface of an insulating part thereof. A palladium conductor layer is formed on the insulating part from a solution for palladium conductor layer formation which contains a palladium compound, an amine compound, and a reducing agent. On the palladium conductor layer is then directly formed a copper deposit by electroplating. Thus, the work is converted to a conductor with the solution for palladium conductor layer formation, which is neutral, without using an electroless copper plating solution which is highly alkaline. Consequently, the polyimide is prevented from being attacked and no adverse influence is exerted on adhesion. By adding an azole compound to the solution for palladium conductor layer formation, a palladium conductor layer is prevented from depositing on copper. Thus, the reliability of connection between the copper part present on a substrate and the copper deposit formed by electroplating is significantly high.

TECHNICAL FIELD

This invention relates to a direct plating process, which can conductelectrolytic copper plating to an insulating part of a workpiece to beplated directly without conducting electroless copper plating, is suitedwhen imparting conductivity to insulating parts of through-holes (TH)and blind via-holes (BVH) of a printed circuit board or the like, and iseffective especially when conducting copper plating to a rigid flexsubstrate or a full-surface resinous build-up substrate having apolyimide as a material, and also to a palladium conductor layer formingsolution for use in the direct plating.

BACKGROUND ART

Seed plating to insulating parts of printed circuit boards hasconventionally been conducted primarily by electroless copper platingprocesses. A representative process is to apply electroless copperplating by adopting, as a pretreatment process, a process that uses aPd—Sn alloy colloid as a catalyst or an alkaline Pd ion solution as acatalyst and conducts metallization of Pd in a solution of a reducingagent in a subsequent step. By this plating process, insulating parts ofmost printed circuit boards can be rendered conductive. There is,however, an increasing difficulty with flexible substrates or rigid flexsubstrates employed in cellular phones, digital cameras, HD or DVDsystems, and the like. As a reason for this increasing difficulty, itcan be mentioned that many electroless copper plating solutions arehighly alkaline and that in these alkaline solutions, polyimidematerials generate functional groups such as amino groups, hydroxylgroups, carbonyl groups and/or carboxyl groups to have hydrophilicityand are hence provided with higher hygroscopicity. Due to this property,long-term treatment with an electroless copper plating solution of highalkalinity results in the penetration of the plating solution into thepolyimide substrate, and subsequent to the plating treatment, thepenetrated plating solution remains between the resulting plating filmand the polyimide substrate and oxidizes the copper, thereby developinga problem that an adhesion failure is induced. In addition, an adhesivelayer employed in such a substrate is prone to dissolution in thealkaline solution and the dissolved matter causes a reduction in thedeposition rate of electroless copper plating, leading to shortening ofthe solution life.

With a view to resolving such problems, there are now many processesmaking use of direct plating that does not use an electroless copperplating solution of high alkalinity and conducts electroplating toworkpieces without applying electroless copper plating.

Japanese Patent No. 2660002 (Patent Document 1) describes a process thatcan apply electroplating by converting a Pd—Sn colloid catalyst into ametal chalcogenide compound film by sulfuration treatment.

Japanese Patent No. 2799076 (Patent Document 2) describes a process thatsubsequent to treatment with a colloidal acidic solution of a noblemetal stabilized with an organic polymer, conducts sulfuration treatmentto effect metal coating under galvanic action.

Japanese Patent No. 3117216 (Patent Document 3) describes a processthat, after a thin oxide film layer is formed in an aqueous solution ofpotassium permanganate which has been adjusted to pH 0 to 6 with asulfonic acid or the like, a conductive polymer layer of a pyrrolederivative is formed, followed by electrolytic plating.

Each of Japanese Patent No. 3284489 (Patent Document 4) and JapanesePatent No. 3261569 (Patent Document 5) describes a process that causes acarbon layer to deposit on a surface, conducts treatment in an acidicsolution to remove carbon from a copper surface, and applieselectrolytic plating.

Practically without exception, however, many of these pretreatmentprocesses require a copper etching step after the step that forms aconductive layer, because in the case of a workpiece composed ofinsulating parts and copper parts as in a printed circuit board havingthrough-holes and/or via-holes, a component employed to form aconductive layer on the copper substitutes or adsorbs, leading to apotential problem of a reduction in the reliability of connectionbetween the copper existing on the substrate and the copper plating filmunless a step is included to remove the component. Further, the copperetching treatment is technically considered to be more difficult than anordinary dissolution step for copper, because the component employed forthe formation of the conductive layers still remains in adhesion on thecopper. Furthermore, the conductive layers applied to the insulatingparts are accompanied by a potential problem that they may be dissolvedor caused to fall off to some extent by the above-described copperetching treatment and also by acid cleaning as pretreatment for coppersulfate plating.

Other patent documents and general publications also include those whichdescribe neutral electroless copper plating solutions. It is, however,the current situation that they have not arrived yet on the market,since they require the use of costly reducing agents and also difficultefforts for the maintenance of solution stability.

Patent Document 1: Japanese Patent No. 2660002

Patent Document 2: Japanese Patent No. 2799076

Patent Document 3: Japanese Patent No. 3117216

Patent Document 4: Japanese Patent No. 3284489

Patent Document 5: Japanese Patent No. 3261569

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

With the foregoing circumstances in view, the present invention has asobjects thereof the provision of a direct plating process for directlyconducting electrolytic copper plating without conducting electrolesscopper plating by forming a palladium conductor layer on an insulatingpart or insulating parts of a workpiece such as a printed circuit boardand also the provision of a palladium conductor layer forming solutionfor use in the direct plating.

Means for Solving the Problems

To achieve the above-described objects, the present inventors haveenthusiastically carried out an investigation, and as a result, havefound that by subjecting a surface of a workpiece, which includes aninsulating part, to palladium catalyst treatment to apply a palladiumcatalyst onto the surface at the insulating part and then forming apalladium conductor layer on the insulating part in a palladiumconductor layer forming solution containing a palladium compound, anamine compound and a reducing agent, while using the thus-appliedpalladium as a catalyst, direct electrolytic copper plating is feasibleon the palladium conductor layer without interposition of an electrolesscopper plating film, also that, although such a process is effective forthe conductivity-imparting treatment of insulating part(s) in aworkpiece in which a section to be subjected to plating includesinsulating part(s) and copper part(s) as in a printed circuit boardhaving through-holes and/or via-holes, the incorporation of an azolecompound in the palladium conductor layer forming solution makes itpossible to selectively form palladium conductor layer(s) on only theinsulating part(s) without formation of palladium conductor layer(s) onthe copper part(s).

Described in further detail, an adverse effect is given to a polyimideof low alkali resistance in conventional electroless copper platingtreatment. Described specifically, it is presumed that an electrolesscopper plating solution of high alkalinity erodes a polyimide surfaceand subsequent to electroless copper plating treatment, exudation of theplating solution onto the polyimide surface oxidizes the electrolesscopper plating film to reduce the adhesion of the plating.

To resolve these problems, the present invention provides a process inwhich subsequent to the application of a palladium catalyst onto aninsulator, a conductor layer of palladium is formed further. Preferably,a palladium catalyst is applied onto an insulator with an acidicpalladium colloid catalyst, and then, a palladium conductor layer isformed in a palladium conductor layer forming solution which contains apalladium compound, an amine compound and a reducing agent. Further,this palladium conductor layer forming solution can form the palladiumconductor layer at near-neutral pH, and the use of a palladium conductorlayer forming solution with an azole compound contained thereinprecludes the formation of a palladium conductor layer onto copper.These can be attributed to the fact that, even if palladium is notapplied or is applied only a little on copper as a result of the use ofan acidic palladium colloid or the like for the application of thepalladium catalyst, this does not cause any substantial problem in thepalladium conductor layer forming treatment and also to the contrivancethat prevents the formation of a palladium conductor layer on the copperowing to the incorporation of the azole compound in the palladiumconductor layer forming solution.

As described above, the present invention conducts the impartation ofconductivity with the above-described neutral palladium conductor layerforming solution without using an electroless copper plating solution ofhigh alkalinity, and therefore, does not erode the polyimide and givesno adverse effect to the adhesion. Further, the palladium conductorlayer may be dried once and may then be subjected to electrolytic copperplating as a next step, instead of using continuous treatment that thepalladium conductor layer is immediately subjected to copper plating. Inaddition, the addition of the azole compound to the palladium conductorlayer forming solution precludes the formation of a palladium conductorlayer on the copper so that the connection between the copper partexisting on the substrate and the electrolytic copper plating film(hereinafter referred to as “copper-copper connection”) is provided withvery high reliability.

It is to be noted that in the conventional patent documents relating toelectroless palladium plating, the dip plating of insulating parts in aplating solution is described to be feasible by imparting catalyticproperties to the insulating parts in accordance with theconventionally-known sensitizing activator method, catalyst acceleratormethod or the like. However, there is not known any undercoating stepthat applies a palladium catalyst to resin parts of an entirety called“a printed circuit board”, such as its surface and TH and BVH, for thepurpose of subsequently conducting the formation of palladium conductorlayers only for obtaining conductivity and further conductingelectrolytic copper plating to the insulating parts such as the resinparts via the palladium conductor layers. There is also unknown thecontrivance that selectively forms palladium conductor layers on onlyinsulating parts and precludes the formation of palladium conductorlayers on metal parts such as copper, that is, a palladium conductorlayer forming solution or electroless palladium plating solutioncontrived to preclude dissolution of the copper existing on the surfaceof a substrate.

The present invention, therefore, provides the following direct platingprocesses and palladium conductor layer forming solutions.

Claim 1:

A direct plating process for applying electrolytic copper plating to aninsulating part of a workpiece having the insulating part, which ischaracterized by subjecting a surface of the workpiece to palladiumcatalyst treatment to apply a palladium catalyst onto the surface at theinsulating part, forming a palladium conductor layer on the insulatingpart with a palladium conductor layer forming solution, which includes apalladium compound, an amine compound and a reducing agent, while usingthe thus-applied palladium as a catalyst, and then forming anelectrolytic copper plating film directly on the palladium conductorlayer.

Claim 2:

The direct plating process according to claim 1, wherein the workpieceis made of a polyimide as a base material.

Claim 3:

The direct plating process according to claim 1 or 2, wherein a sectionof the workpiece, the section being to be subjected to the platingtreatment, includes an insulating part and a copper part, the palladiumconductor layer forming solution further includes an azole compound, andby treating the workpiece with the palladium conductor layer formingsolution, a palladium conductor layer is selectively formed on only theinsulating part without formation of the palladium conductor layer onthe copper part.

Claim 4:

The direct plating process according to claim 3, wherein the azolecompound is benzotriazole.

Claim 5:

The direct plating process according to claim 3 or 4, wherein theworkpiece is a printed circuit board having through-holes and/orvia-holes.

Claim 6:

The direct plating process according to any one of claims 1-5, whereinthe palladium conductor layer forming solution has a pH not higher than8.

Claim 7:

The direct plating process according to any one of claims 1 to 6,wherein the application of the palladium catalyst is conducted bytreatment with an acidic palladium colloid solution dispersed andstabilized with an organic polymer.

Claim 8:

A palladium conductor layer forming solution for use in direct plating,is characterized by including a palladium compound, an amine compoundand a reducing agent.

Claim 9:

The palladium conductor layer forming solution according to claim 8,which further includes an azole compound.

Claim 10:

The palladium conductor layer forming solution according to claim 9,wherein the azole compound is benzotriazole.

Claim 11:

The palladium conductor layer forming solution according to any one ofclaims 8 to 10, which has a pH not higher than 8.

EFFECTS OF THE INVENTION

The direct plating process and palladium conductor layer formingsolution according to the present invention have the followingadvantageous effects.

(1) A conductor layer (palladium conductor layer) is formed in a shorttime in a neutral solution, and therefore, no penetration of thesolution into polyimide takes place even when a workpiece made of apolyimide base material is used.(2) The conductor layer on the polyimide is formed with palladium, andtherefore, no metal oxide is generated with time so that the conductorlayer is excellent in adhesion.(3) Palladium is more resistant to oxidation than copper, and therefore,sufficient conductivity is obtained with a layer thickness of 5 to 50 nmor so and no long hours dipping in the treatment solution is needed.(4) Palladium is superior in corrosion resistance to copper, andtherefore, long term storage is feasible after the formation of thepalladium conductor layer until electrolytic copper plating treatmentsuch as copper sulfate plating.(5) A step by conventional electroless copper plating pretreatment canalso be used.(6) The use of a palladium conductor layer forming solution with anazole compound contained therein obviates etching after the formation ofa conductor layer, because no conductor layer exists on a copper part ofa surface of a workpiece.(7) The reliability of copper-copper connection is high, since noconductor layer exists on the copper part as mentioned above.

BEST MODES FOR CARRYING OUT THE INVENTION

As mentioned above, the direct plating process according to the presentinvention is to form an electrolytic copper plating film on aninsulating part of a workpiece. By subjecting the workpiece to palladiumcatalyst treatment at a surface thereof, a palladium catalyst is appliedto the surface at the insulating part. Using the thus-applied palladiumas a catalyst, a palladium conductor layer is then formed with apalladium conductor layer forming solution which contains a palladiumcompound, an amine compound and a reducing agent. Subsequently, anelectrolytic copper plating film is formed directly on the palladiumconductor layer at the insulating part.

The workpiece can be one in which a section to be subjected to platingtreatment is insulating in its entirety, or can be one in which asection to be subjected to plating treatment includes both an insulatingpart and a copper part, for example, a printed circuit board or the likehaving a copper film with through-holes and/or via-holes formedtherethrough, specifically a rigid flex substrate, full-surface resinousbuild-up substrate or like substrate having a polyimide as a material.

In the present invention, conventional methods can be adopted for thepretreatment steps up to the palladium catalyst treatment. In the caseof a printed circuit board having a copper film, for example, it ispossible to adopt such a process that after conducting conditioning withan alkaline cleaner such as amine compounds including a nonionicsurfactant and/or cationic surfactant, copper etching is conducted withan etchant containing an oxidizing agent and an acid, followed by acidcleaning or the like.

Further, the palladium catalyst treatment to the insulating part of theworkpiece can also be conducted by a known method, for example, by usingone of the sensitizing activator method, the Pd—Sn colloid catalyst, analkaline Pd ion catalyst and an acidic Pd colloid catalyst, all of whichare known conventionally.

In this case, the most preferred in view of shortening of the number ofsteps and cost is an acidic Pd colloid solution dispersed and stabilizedwith an organic polymer, because the Pd—Sn colloid catalyst requires astep for the removal of Sn which has a potential problem of impairingthe reliability of copper-copper connection and the alkaline Pd ioncatalyst requires a Pd-reducing step after the treatment.

It is to be noted that as an activator for use in the application ofsuch a palladium catalyst, an activator can be prepared with a knowncomposition or a commercial product can be used. As conditions for thetreatment with the activator, known usual conditions can be adopted.

Next, the palladium conductor layer forming solution for the formationof the palladium conductor layer contains a palladium compound in a formcomplexed with an amine compound and also a reducing agent.

As the palladium compound to be used, a known palladium compound can beused, and a water-soluble palladium compound such as palladium oxide,palladium chloride, palladium nitrate, palladium acetate, sodiumpalladium chloride, potassium palladium chloride, ammonium palladiumchloride, palladium sulfate or tetraamminepalladium chloride can bementioned. The use concentration of the palladium compound maypreferably in a range of 0.0001 to 0.01 mol/L, with 0.0005 to 0.002mol/L being most preferred. At a concentration lower than 0.0001 mol/L,the rate at which a palladium conductor layer is formed becomes slower.When the concentration is excess of 0.01 mol/L, on the other hand, theprocess becomes costly in economy, and at a palladium concentrationhigher than 0.01 mol/L, there is a potential problem that palladium maysubstitute or precipitate on copper.

The palladium conductor layer forming solution for use in the presentinvention may preferably use at least one kind of amine compound tostably form and maintain a complex of palladium. As the pH of thepalladium conductor layer forming solution is maintained around 7 inthis case, a compound capable of stably forming a complex at the pH isselected. The concentration of the amine compound may be preferably0.0001 to 0.1 mol/L, more preferably 0.001 to 0.02 mol/L. The aminecompound contributes more to the stability of the solution as itsconcentration becomes higher. At a concentration higher than 0.1 mol/L,however, the amine compound exhibits stronger dissolution power for thecopper on the substrate so that the concentration of copper in thepalladium conductor layer forming solution rises. When the concentrationof copper rises, the formation rate of the conductor layer drops,leading to a potential problem that the life of the palladium conductorlayer forming solution may be shortened. At a concentration lower than0.0001 mol/L, on the other hand, no palladium complex is formed, leadingto a potential problem that the palladium conductor layer formingsolution may be brought into a suspended state and may eventually form aprecipitate.

Examples of the amine compound include monoamines such as methylamine,ethylamine, propylamine, trimethylamine and dimethylethylamine, diaminessuch as methylenediamine, ethylenediamine, tetramethylenediamine andhexamethylenediamine, polyamines such as diethylenetriamine,triethylenetetramine and pentaethylenehexamine, and in addition, aminoacids and the like such as ethylenediaminetetraacetic acid and itssodium salt, potassium salt and ammonium salt, nitrilotriacetic acid andits sodium salt, potassium salt and ammonium salt, glycine, andiminodiacetic acid.

For an improvement in stability, it is also desired to add an aliphaticcarboxylic acid. Illustrative are monocarboxylic acids such as formicacid, acetic acid, propionic acid, butyric acid, isobutyric acid,valeric acid and isovalelic acid, dicarboxylic acids such as oxalicacid, malonic acid, succinic acid, glutaric acid, maleic acid, fumaricacid, citraconic acid, itaconic acid, and other carboxylic acids such astricarballylic acid, glycolic acid, lactic acid, malic acid, tartaricacid, citric acid, isocitric acid, alloisocitric acid, gluconic acid,oxalacetic acid and diglycolic acid, and the sodium salts, potassiumsalts, ammonium salts and the like of these carboxylic acids.

One or more of the above-described carboxylic acids and salts can beused. Its concentration may be preferably 0.0001 to 0.1 mol/L, morepreferably 0.001 to 0.02 mol/L. At a concentration lower than 0.0001mol/L, its effect as a stabilizer is weak. At a concentration higherthan 0.1 mol/L, on the other hand, its role as a stabilizer is saturatedso that such a high concentration requires wasteful cost and is notpractical from the standpoint of economy.

As the reducing agent, a known reducing agent can be used. Illustrativeare hypophosphorous acid and its salts, boron hydride and its salts,dimethylamineboran, trimethylamineboran, hydrazine, and the like.

The above-described reducing agent acts as a reducing agent forpalladium ions in the palladium conductor layer forming solution for usein the present invention, and its concentration may be preferably 0.01to 1 mol/L, more preferably 0.05 to 0.5 mol/L. A concentration lowerthan 0.01 mol/L leads to a reduction in reaction velocity, while aconcentration higher than 1 mol/L has a potential problem that thepalladium conductor layer forming solution may become unstable.

To avoid the formation of a palladium conductor layer on the surface ofeach copper part of the workpiece, it is preferred to add an azolecompound to the palladium conductor layer forming solution for use inthe present invention. The azole compound is adsorbed on the copper tosuppress the dissolution of the copper by the amine, thereby inhibitingthe substitution reaction of palladium onto the copper so that apalladium conductor layer is formed on the insulating part only.

Examples of the azole compound for use in the present invention includeimidazoles such as imidazole, 2-phenylimidazole, 1-vinylimidazole,benzoimidazole, 2-butylbenzoimidazole, 2-phenylethylbenzoimidazole and2-aminobenzoimidazole, triazoles such as 1,2,4-triazole,3-amino-1,2,4-triazole, 1,2,3-benzotriazole, 1-hydroxybenzotriazole andcarboxybenzotriazole, tetrazoles such as tetrazole,5-phenyl-1H-tetrazole, 5-methyl-1H-tetrazole and 5-amino-1H-tetrazole,pyrazole, and benzothiazole. 1,2,3-benzotriazole is particularlypreferred.

Two or more of the above-described azole compounds may be used incombination. The concentration of the azole compound may be preferably0.0001 to 0.2 mol/L, more preferably 0.0002 to 0.02 mol/L. At aconcentration lower than 0.0001 mol/L, the substitution or precipitationof palladium on copper takes place, leading to the potential problemthat the reliability of copper-copper connection may be impaired. Or,there is the possibility that the formation of a palladium conductorlayer may not be smoothly conducted due to the dissolution of copperinto the solution. A concentration higher than 0.2 mol/L causes noproblem insofar as the azole compound is dissolved, but is not practicalfrom the standpoint of cost.

The palladium conductor layer forming solution for use in the presentinvention can be used suitably at pH 8 or lower, notably at a pH rangeof 6 to 8. In this pH range, a good palladium conductor layer can beformed. At lower than pH 6, the formation of an amine complex issuppressed so that a difficulty may arise in the formation of apalladium conductor layer. When the pH exceeds 8, on the other hand, thedissolution of copper takes place, leading to a potential problem thatthe formation of a conductor layer on an insulating material may besuppressed. As the treatment temperature, a range of 20 to 80° C. can beused. Especially at 40° C. or higher, a good palladium conductor layercan be formed in a short time. At lower than 20° C., the reaction maynot initiate in some instances, and no uniform palladium conductor layermay be formed accordingly. When the treatment temperature exceeds 80°C., the stability of the solution may be lowered in some instances. Itis to be noted that the treatment time with the palladium conductorlayer forming solution may be preferably 0.5 to 5 minutes, notably 1 to3 minutes or so.

In the present invention, a palladium conductor layer is formed in thepalladium conductor layer forming solution, which contains theabove-described reducing agent, while using as a catalyst the palladiumapplied to the insulating part. In this case, the palladium conductorlayer has a thickness of 5 to 50 nm or so, and has conductivitysufficient to conduct electrolytic copper plating. By adding the azolecompound, the compound adheres to the copper and protects it, therebyreducing the copper-dissolving action of the palladium conductor layerforming solution and the substitution and deposition of palladium. As aconsequence, it is possible to assure high reliability for thecopper-copper connection.

After the palladium conductor layer is formed as described above, copperplating is conducted. Since the palladium conductor layer has alreadybeen formed on the insulating part of the workpiece in this case,electrolytic copper plating can be conducted directly onto the palladiumconductor layer without additionally applying electroless copper platingto the insulating part. In particular, it is unnecessary to interpose anelectroless copper plating which uses an alkaline electroless copperplating solution.

The plating solution for use in such electrolytic copper plating canhave a known composition, and a commercial product can be used. Further,as conditions for the plating, known usual conditions can be adopted. Itis to be noted that the electrolytic copper plating may preferably be,but is not limited to, copper sulfate plating.

EXAMPLES

Examples and Comparative Examples will hereinafter be given tospecifically describe the present invention. It is, however, to be notedthat the present invention is not limited to the following Examples.

As steps up to the application of a palladium catalyst before theformation of a palladium conductor layer, the steps No. 1 to No. 3 shownin Table 1 were conducted separately. As palladium conductor layerforming solutions for forming palladium conductor layers, those havingthe compositions A to D shown in Table 2 were employed separately.

TABLE 1 Step No. 1 No. 2 No. 3 Cleaning “WCD”⁽¹⁾: 50 mL/L “WCD”⁽¹⁾: 50mL/L “WCD”⁽¹⁾: 50 mL/L 50° C. × 5 min 50° C. × 5 min 50° C. × 5 minHot-water 50° C. × 1 min 50° C. × 1 min 50° C. × 1 min rinsing Waterrinsing Room temp. × 1 min Room temp. × 1 min Room temp. × 1 min Etching35% H₂O₂: 50 mL/L 35% H₂O₂: 50 mL/L 35% H₂O₂: 50 mL/L 62.5% H₂SO₄: 160mL/L 62.5% H₂SO₄: 160 mL/L 62.5% H₂SO₄: 160 mL/L “MSE-7”⁽²⁾: 50 mL/L“MSE-7”⁽²⁾: 50 mL/L “MSE-7”⁽²⁾: 50 mL/L 40° C. × 2 min 40° C. × 2 min40° C. × 2 min Water rinsing Room temp. × 1 min Room temp. × 1 min Roomtemp. × 1 min Acid cleaning 62.5% H₂SO₄: 100 mL/L 62.5% H₂SO₄: 100 mL/L62.5% H₂SO₄: 100 mL/L Room temp. × 1 min Room temp. × 1 min Room temp. ×1 min Water rinsing Room temp. × 1 min Room temp. × 1 min Room temp. × 1min Pre-dipping — — “PED-104”⁽⁹⁾: 270 g/L 25° C. × 2 min Catalyst“WAT”⁽³⁾: 50 mL/L “MAT-2A”⁽⁵⁾: 200 mL/L “AT-105”⁽¹⁰⁾: 30 mL/L treatment“WHP”⁽⁴⁾: 5 mL/L “MAT-2B”⁽⁶⁾: 40 mL/L “PED-104”⁽⁹⁾: 270 g/L 40° C. × 5min 60° C. × 5 min 30° C. × 8 min Water rinsing Room temp. × 1 min Roomtemp. × 1 min Room temp. × 1 min Sn removal — — “AT-106”⁽¹¹⁾: 100 mL/L25° C. × 3 min Water rinsing — — Room temp. × 1 min Reduction —“MAB-4A”⁽⁷⁾: 20 mL/L — “MAB-4B”⁽⁸⁾: 200 mL/L 35° C. × 3 min Waterrinsing — Room temp. × 1 min — ⁽¹⁾An alkaline solution of aminecompounds including a nonionic surfactant and a cationic surfactant ⁽²⁾Astabilizer for hydrogen peroxide ⁽³⁾An acidic palladium colloid solution(palladium solution) ⁽⁴⁾An acidic palladium colloid solution (reducingagent) ⁽⁵⁾An alkaline solution of a palladium complex (palladiumsolution) ⁽⁶⁾An alkaline solution of a palladium complex (chelatingagent) ⁽⁷⁾A dimethylamineboran solution ⁽⁸⁾A pH adjuster (buffer) ⁽⁹⁾APd—Sn colloid solution (stabilizer) ⁽¹⁰⁾A Pd—Sn colloid solution (Pd—Snsolution) ⁽¹¹⁾A boron fluoride solution * The chemicals (1) to (11) areproducts of C. Uyemura & Co., Ltd.

TABLE 2 A B C D PdCl₂ 185 ppm PdCl₂ 370 ppm Pd(NH₃)₄Cl₂ 370 ppmPd(NH₃)₄Cl₂ 370 ppm EDA⁽¹²⁾ 1 g/L EDA 2 g/L EDA 2 g/L EDA 2 g/L BTA⁽¹³⁾100 ppm BTA 200 ppm BTA 200 ppm Na hypo- 5 g/L Na hypo- 5 g/L Na hypo- 5g/L Na hypo- 5 g/L phosphite phosphite phosphite phosphite Maleic 1 g/LFumaric 1 g/L Succinic 1 g/L Maleic 1 g/L acid acid acid acid⁽¹²⁾Ethylenediamine ⁽¹³⁾1,2,3-Benzotriazole

Example 1

The palladium conductor layer forming solution slightly dissolves copperowing to the amine compound. As a result of the dissolution of copper, acopper complex is formed. By the copper complex, the formation of apalladium conductor layer is suppressed so that no good and conductivepalladium conductor layer can be obtained. Azole compounds weretherefore added as chemicals that suppress the dissolution of copper. Tosolutions shown under “D” in Table 2, BTA (1,2,3-benzotriazole),triazole, hydroxybenzotriazole and phenylbenzotriazole were added at0.002 mol/L, respectively, and in 500 mL aliquots of the resultingsolutions, FR-4 substrates were dipped over 1 dm², respectively, andwere left over at 50° C. for 14 hours. As a result, copper-dissolutionsuppressing effect was observed on the solutions with the correspondingazole compounds added in the same amount therein in comparison with thesolution to which no azole compound was added. Especially on BTA, thiseffect was observed pronouncedly. The results are shown in Table 3.

TABLE 3 Not Hydroxy- Phenyl- added BTA Triazole benzotriazolebenzotriazole Amount of copper 49.8 2.7 33.3 26.3 10.2 dissolved (ppm)Dissolution rate 3.5 0.2 2.4 1.9 0.7 of copper (ppm/hr)

Example 2

A specimen, which had been prepared by completely dissolving off asurface-laminated copper foil from a commercial product (FR-4) throughetching, and two types of 75-μm polyimide films (“KAPTON,” product ofE.I. du Pont de Nemours and Company; and “UPILEX,” product of UbeIndustries, Ltd.) were treated with the Sn-free, acidic palladiumcolloid solution shown under No. 1 in Table 1, and palladium conductorlayers were then formed under the conditions of pH 7, 50° C. and 2minutes in the palladium conductor layer forming solution shown under“A” in Table 2. As a result, the palladium conductor layers were formedwith a thickness of 8 nm on the resins of all of the FR-4 and the twotypes of polyimide films, respectively, and were found to have 500 mΩ asconduction resistance across 100 mm (width: 50 mm). In tape tests, thosepalladium conductor layers were confirmed to remain free from peeling.

Subsequently, electrolytic copper plating was conducted to 25 μm at acathode current density of 2.5 A/dm² in an electrolytic copper platingsolution which contains copper sulfate pentahydrate (80 g/L), sulfuricacid (200 g/L), chloride ions (60 ppm), and “EPL-1-4A” (0.5 mL/L) and“EPL-1-B” (20 mL/L) [additives for cupper sulfate plating; products ofC. Uyemura & Co., Ltd.]. Copper was completely applied onto the entiresurfaces of the resins of all of the FR-4 and the two types of polyimidefilms. Further, those samples were subjected at 150° C. for 1 hour toheat treatment, but no blister occurred.

Example 3

With respect to a commercial product (FR-4 substrate) (0.3 mm indiameter, 1.6 mm in thickness), a two-layered polyimide plate (material:“UPILEX”) and a three-layered polyimide plate (material: “KAPTON”) inall of which through-holes were formed, similar treatments as in Example2 were conducted up to copper sulfate plating. As a result, coppersulfate plating films were completely applied into the through-holeswithout any problem.

Example 4

A specimen, which had been prepared by completely dissolving off asurface-laminated copper foil from a commercial product (FR-4) throughetching, and two types of 75-μm polyimide films (“KAPTON” and “UPILEX”)were treated with the alkaline palladium-complex solution with theSn-free shown under No. 2 in Table 1, and palladium conductor layerswere then formed under the conditions of pH 7, 50° C. and 2 minutes inthe palladium conductor layer forming solution shown under “B” in Table2. As a result, the palladium conductor layers were formed with athickness of 8 nm on the resins of all of the FR-4 and the two types ofpolyimide films, respectively, and were found to have 1 kΩ as conductionresistance across 100 mm (width: 50 mm). In tape tests, those palladiumconductor layers were confirmed to remain free from peeling.

Subsequently, electrolytic copper plating was conducted to 25 μmthickness at a cathode current density of 2.5 A/dm² in an electrolyticcopper plating solution which contains copper sulfate pentahydrate (80g/L), sulfuric acid (200 g/L), chloride ions (60 ppm), and “EPL-1-4A”(0.5 mL/L) and “EPL-1-B” (20 mL/L) [additives for cupper sulfateplating; products of C. Uyemura & Co., Ltd.]. Copper was completelyapplied onto the entire surfaces of the resins of all of the FR-4 andthe two types of polyimide films. Further, those samples were subjectedat 150° C. for 1 hour to heat treatment, but no blister occurred.

Example 5

With respect to a commercial product (FR-4 substrate) (0.3 mm indiameter, 1.6 mm in thickness), a two-layered polyimide plate (material:“UPILEX”) and a three-layered polyimide plate (material: “KAPTON”) inall of which through-holes were formed, similar treatments as in Example4 were conducted up to copper sulfate plating. As a result, coppersulfate plating films were completely applied into the through-holeswithout any problem.

Example 6

A specimen, which had been prepared by completely dissolving off asurface-laminated copper foil from a commercial product (FR-4) throughetching, and two types of 75-μm polyimide films (“KAPTON” and “UPILEX”)were treated with the Pd—Sn colloid solution shown under No. 3 in Table1, and palladium conductor layers were then formed under the conditionsof pH 7, 50° C. and 2 minutes in the palladium conductor layer formingsolution shown under “C” in Table 2. As a result, the palladiumconductor layers were formed with a thickness of 10 nm on the resins ofall of the FR-4 and the two types of polyimide films, respectively, andwere found to have 830 mΩ as conduction resistance across 100 mm (width:50 mm). In tape tests, those palladium conductor layers were confirmedto remain free from peeling.

Subsequently, electrolytic copper plating was conducted to 25 μmthickness at a cathode current density of 2.5 A/dm² in an electrolyticcopper plating solution which contains copper sulfate pentahydrate (80g/L), sulfuric acid (200 g/L), chloride ions (60 ppm), and “EPL-1-4A”(0.5 mL/L) and “EPL-1-B” (20 mL/L) [additives for cupper sulfateplating; products of C. Uyemura & Co., Ltd.]. Copper was completelyapplied onto the entire surfaces of the resins of all of the FR-4 andthe two types of polyimide films. Further, those samples were subjectedat 150° C. for 1 hour to heat treatment, but no blister occurred.

Example 7

With respect to a commercial product (FR-4 substrate) (0.3 mm indiameter, 1.6 mm in thickness), a two-layered polyimide plate (material:“UPILEX”) and a three-layered polyimide plate (material: “KAPTON”) inall of which through-holes were formed, similar treatments as in Example6 were conducted up to copper sulfate plating. As a result, coppersulfate plating films were completely applied into the through-holeswithout any problem.

Comparative Example 1

Two types of 75-μm polyimide films (“KAPTON” and “UPILEX”) were treatedwith the Pd—Sn colloid solution shown under No. 3 in Table 1, and werethen subjected to electroless copper plating under the conditions of 35°C. and 20 minutes with a general electroless copper plating solution. Asa result, copper plating films were formed on the entire surfaceswithout blister. However, those films had no adhesion with thepolyimide, and were confirmed to be instantaneously peeled off in tapetests.

Comparative Example 2

A specimen, which had been prepared by completely dissolving off asurface-laminated copper foil from a commercial product (FR-4) throughetching, and two types of 75-μm polyimide films (“KAPTON” and “UPILEX”)were treated with the acidic Pd colloid solution shown under No. 1 in

Table 1, and their conduction resistances across 100 mm (width: 50 mm)were measured without conducting any palladium conductor layer formingtreatment. However, no conductivity was obtained and the measurement wasimpossible.

Subsequently, electrolytic copper plating was conducted to 25 μmthickness at a cathode current density of 2.5 A/dm² in an electrolyticcopper plating solution which contains copper sulfate pentahydrate (80g/L), sulfuric acid (200 g/L), chloride ions (60 ppm), and “EPL-1-4A”(0.5 mL/L) and “EPL-1-B” (20 mL/L) [additives for cupper sulfateplating; products of C. Uyemura & Co., Ltd.]. No copper plating filmdeposited on the resins of all of the FR-4 and the two types ofpolyimide films.

1. A direct plating process for applying electrolytic copper plating toan insulating part of a workpiece having said insulating part which ischaracterized by: subjecting a surface of said workpiece to palladiumcatalyst treatment to apply a palladium catalyst onto said surface atthe insulating part; forming a palladium conductor layer on saidinsulating part with a palladium conductor layer forming solution, whichcomprises a palladium compound, an amine compound and a reducing agent,while using the thus-applied palladium as a catalyst; and then formingan electrolytic copper plating film directly on said palladium conductorlayer.
 2. The direct plating process according to claim 1, wherein saidworkpiece is made of a polyimide as a base material.
 3. The directplating process according to claim 1 or 2, wherein a section of saidworkpiece, said section being to be subjected to said plating treatment,comprises an insulating part and a copper part, said palladium conductorlayer forming solution further comprises an azole compound, and bytreating said workpiece with said palladium conductor layer formingsolution, a palladium conductor layer is selectively formed on only saidinsulating part without formation of said palladium conductor layer onsaid copper part.
 4. The direct plating process according to claim 3,wherein said azole compound is benzotriazole.
 5. The direct platingprocess according to claim 3, wherein said workpiece is a printedcircuit board having through-holes and/or via-holes.
 6. The directplating process according to claim 1, wherein said palladium conductorlayer forming solution has a pH not higher than
 8. 7. The direct platingprocess according to claim 1, wherein the application of said palladiumcatalyst is conducted by treatment with an acidic palladium colloidsolution dispersed and stabilized with an organic polymer.
 8. Apalladium conductor layer forming solution for use in direct plating, ischaracterized by comprising a palladium compound, an amine compound anda reducing agent.
 9. The palladium conductor layer forming solutionaccording to claim 8, which further comprises an azole compound.
 10. Thepalladium conductor layer forming solution according to claim 9, whereinsaid azole compound is benzotriazole.
 11. The palladium conductor layerforming solution according to any one of claims 8 to 10, which has a pHnot higher than 8.